The present invention relates generally to the packaging of electronic components. More particularly, the present invention relates to method for forming an image sensor assembly.
Methods for forming image sensors and assemblies are well known to those of skill in the art. Prior art image sensors typically included an active area, which was responsive to electromagnetic radiation. In prior art image sensor assemblies, an image sensor was located within a housing that supported a window. Radiation passed through the window and struck the active area of the image sensor, which responded to the radiation. For the image sensor to function properly, the image sensor had to be positionally aligned with the window to within tight tolerances.
In the prior art, an image sensor assembly was formed by mounting the image sensor to a printed circuit motherboard. After the image sensor was mounted, a housing was mounted around the image sensor and to the printed circuit motherboard. This housing provided a seal around the image sensor, while at the same time, supported a window above the image sensor.
Beaman et al., U.S. Pat. No. 5,821,532, hereinafter Beaman, which is herein incorporated by reference in its entirety, is one example of a prior art image sensor assembly. Beaman sets forth a printed circuit board that included a pair of apertures used as alignment features for mounting the image sensor and for mounting the optics that included the window. More particularly, the pair of apertures were used as the mounting reference for the image sensor and then were used as the mounting reference for the optics.
As discussed in Beaman, prior art image sensor assemblies used a housing to support the window and to hermetically seal the image sensor (see housing 24 and window 25 of Beaman FIG. 4 for example). This housing was typically formed of ceramic that advantageously had excellent resistance to moisture transmission to protect the image sensor from the ambient environment. However, ceramic is relatively expensive compared to other packaging materials and, in the current market, it is critical to form the image sensor assembly at minimal cost.
In addition to using relatively expensive ceramics, the prior art ceramic image sensor assemblies were also very labor intensive and expensive to produce. For instance, after the prior-art ceramic image sensor assembly was constructed, the lens assembly was placed over the image sensor assembly. Typically, the lens assembly was attached directly to the substrate after the image sensor assembly was attached to the substrate. After attachment, the lens assembly was adjusted, for example with adjustment screws, to move the lens assembly until the proper focus was attained. This rough adjustment was very labor intensive. Further, a large tolerance was associated with this very rough adjustment.
In addition, mounting the housing at the printed circuit board level, as was done in the prior art, was itself inherently labor intensive and made repair or replacement of the image sensor difficult. In particular, removal of the housing exposed the image sensor to the ambient environment. Since the image sensor was sensitive to dust as well as other environmental factors, mounting the housing at the printed circuit board level made it mandatory to make repairs, or to replace, the image sensor in a controlled environment such as a clean room, otherwise there was a risk of damaging or destroying the image sensor. Thus, using the prior art method of mounting the housing at the printed circuit board level often meant transporting the entire motherboard into the clean room.
To overcome the problems with prior art ceramic image sensor assemblies discussed above, image sensor packages have recently been introduced that include a molding with an interior locking feature and an exterior locking feature. One example of a prior art molded image sensor assembly is set forth in the commonly assigned U.S. patent application Ser. No. 09/457,505 entitled xe2x80x9cMOLDED IMAGE SENSOR PACKAGExe2x80x9d, listing Steven Webster as inventor, filed on Dec. 8, 1999, hereinafter referred to as the Webster reference, which is incorporated herein for all purposes, and in its entirety, by reference.
The interior locking feature and the exterior locking feature of prior art molded image sensor assemblies allowed the package to be made of a molding, typically plastic, that was a low cost part. The Webster image sensor package further included a window having an interior surface and an exterior surface. The exterior locking feature of the molding contacted a periphery of the exterior surface of the window and the interior locking feature of the molding -contacted a periphery of the interior surface of the window. In this manner, the window was supported by the molding both top and bottom. In addition, the distance which moisture had to travel along the interface between the molding and window to reach the image sensor was maximized, thus essentially eliminating moisture ingress into the image sensor package.
As a result, the prior art molded image sensor assemblies, such as the Webster image sensor package, did not suffer from the high costs associated with ceramic assemblies nor were they labor intensive or require large tolerances. In addition, the prior art molded image sensor assemblies, such as the Webster image sensor package, did not involve mounting the housing at the printed circuit board level. Consequently, these prior art molded image sensor assemblies were a marked improvement over the prior art ceramic image sensor assemblies.
While prior art molded image sensor assemblies represented a significant improvement over the ceramic prior art assemblies, the prior art molded image sensor assemblies were typically relatively large. This was because, in prior art molded image sensor assemblies, the image sensor chip was typically electrically connected to the motherboard using a support substrate and bond wires connecting bond pads on the image sensor chip to bonding locations on the substrate. The substrate was then, in turn, electrically connected to the motherboard. Consequently, extra structure, i.e., an extra substrate, and bond wires, both of which added significantly to the cost and the size of prior art molded image sensor assemblies, were required. In addition, the bond wires themselves were susceptible to breaking and the image sensor assembly therefore suffered from decreased reliability.
As the electronics industry has moved to smaller and lighter weight electronic devices, it has become increasingly important that the size of the image sensor assembly used within these electronic devices be minimized. However, as discussed above, the prior art molded image sensor assemblies used bond wire connections, which were inherently bulky and expensive. As a result, the prior art molded image sensor assemblies were relatively large and expensive to produce.
In the prior art it was well known that, theoretically, a more ideal method of connecting an image sensor assembly to a motherboard would be to connect the image sensor chip to a lead frame or a Land Grid Array (LGA) directly in a flip-chip configuration. Then the lead frame and sensor could be packaged in an assembly and electrically connected to the motherboard. If this structure were possible, then the extra substrate and bond wires of the prior art molded image sensor assemblies could be eliminated while, at the same time, the image sensor assembly cost, image sensor assembly reliability and image sensor assembly size could be improved.
FIG. 1 shows a top plan view of a lead frame 10 including: frame 11; internal connection leads 12; and external connection leads 13. While the flip-chip structure discussed above sounded advantageous in theory, in practice, it was found that connecting an image sensor die to internal connection leads 12 of lead frame 10 in a flip-chip configuration was prohibitively difficult, and often impossible. This was because internal connection leads 12, external connection leads 13 and frame 11 of lead frame 10 were too delicate and would bend, deform and/or break as the image sensor die was being attached. In addition, external connection leads 13 would also bend, deform and/or break as the image sensor assembly was being attached to an external unit such as a circuit board or motherboard.
As a result, proper connections were not made, internal and external connection leads 12 and 13 broke and the resulting structures were often warped and suffered from unacceptably poor reliability. Consequently, in the prior art, molded image sensor assemblies almost exclusively used the bond wire connections and included the standard bond wire connection substrates discussed above. As a result, prior art molded image sensor assemblies were more expensive, less reliable, larger and more delicate than ideal.
What is needed is an image sensor assembly, which is simpler and less expensive to manufacture, easier to service, smaller and more reliable than either prior art ceramic image sensor assemblies or prior art molded image sensor assemblies.
According to the present invention, a method for forming an image sensor assembly includes integrally forming a lead frame or Land Grid Array (LGA) into a molded image sensor die package so that the lead frame or LGA is fully supported and structurally fortified by the molded image sensor die package. An image sensor die is then attached to the thus supported lead frame or LGA using a standard flip-chip connection.
The image sensor assemblies formed by the method of the invention include a molded image sensor package. Consequently, like the Webster image sensor packages of the prior art discussed above, the image sensor assemblies of the invention do not suffer from the high costs associated with ceramic assemblies nor are they labor intensive or require large tolerances. In addition, the image sensor assemblies formed by the methods of the invention, like the Webster image sensor package of the prior art, do not involve mounting the housing at the printed circuit board level. Consequently, the image sensor assemblies of the invention are a significant improvement over the prior art ceramic image sensor assemblies.
In addition, and in contrast to prior art molded image sensor assemblies such as the Webster package, according to methods of the invention, the lead frame or LGA is integrally formed into a molded image sensor die package so that the lead frame or LGA is fully supported and structurally fortified by the molded image sensor die package. Consequently, the problems of bending, deformation and/or breaking of the lead frame or LGA during image sensor die attachment are avoided. As a result, proper connections are made, leads do not break, the connections are not stressed and the resulting structures are not warped nor do they suffer from poor reliability.
Thus, using the method of the invention, molded image sensor assemblies can utilize flip-chip connections and avoid the costly, and bulky, bond wire connections of the prior art that included the standard bond wire connection substrates discussed above. As a result, molded image sensor assemblies of the invention are less expensive, more reliable, smaller and sturdier than prior art molded image sensor assemblies.
In particular, one embodiment of the invention for packaging an image sensor includes forming an image sensor die package that includes: an optical element support, the optical element support defining an aperture with an optical centerline; and an external connection assembly, the external connection assembly being an integral part of the image sensor die package.
The method also includes positioning in the image sensor package optical element support an optical element which includes an optical element first surface and an optical element second surface, opposite the optical element first surface, the optical element being positioned in the image sensor package optical element support such that the optical element first surface and the optical element second surface are approximately perpendicular to the optical centerline.
An image sensor die is then provided that includes an image sensor die first surface and an image sensor die second surface, opposite the image sensor die first surface, the image sensor die first surface having an active region.
The image sensor die first surface is then electrically coupled to a first portion of the external connection assembly in a flip-chip configuration such that the active region of the first surface of the image sensor die is at least partially aligned with the optical element support aperture and the optical centerline so that at least a potion of the active region faces the second surface of the optical element.
In one embodiment of the method of the invention, the image sensor die package is formed such that the external connection assembly is a lead frame including internal connection leads and external connection leads and the image sensor die is electrically coupled to the internal connection leads in a flip-chip configuration.
In one embodiment of the method of the invention, the image sensor die package is formed of molded plastic, the image sensor die package being molded around a portion of the lead frame such that the portion of the lead frame is molded into the image sensor die package.
In one embodiment of the method of the invention, the molded image sensor die package is formed to include a base and an optical element support housing including the optical element support.
In one embodiment of the method of the invention, the image sensor die package is formed such that the external connection assembly is a land grid array that includes internal connection points and external connection points and the image sensor die is electrically coupled to the internal connection points in a flip-chip configuration. In one embodiment of the method of the invention, the image sensor die package is formed of molded plastic package, the image sensor die package being molded over the land grid array such that the land grid array is formed on a first surface of the image sensor die package.
In one embodiment of the method of the invention, the image sensor die package is formed to include a base and an optical element support housing including the optical element support and the land grid array is formed on a first surface of the image sensor die package base.
In one embodiment of the invention, a method for packaging an image sensor includes providing an adjustable focus image sensor die package that includes: an optical element support, the optical element support defining an optical element support aperture with an optical centerline; an optical element support housing, the optical element support housing defining an optical element support housing aperture with the same the optical centerline; and an external connection assembly, the external connection assembly being an integral part of the adjustable focus image sensor die package
An optical element is included with an optical element first surface and an optical element second surface, opposite the optical element first surface, the optical element being positioned in the optical element support such that the optical element first surface and the optical element second surface are approximately perpendicular to the optical centerline.
An image sensor die is provided that includes an image sensor die first surface and an image sensor die second surface, opposite the image sensor die first surface, the image sensor die first surface having an active region.
The image sensor die first surface is then electrically coupled to a first portion of the external connection assembly in a flip-chip configuration such that the active region of the first surface of the image sensor die is at least partially aligned with the optical element support aperture and the optical centerline so that at least a portion of the active region faces the second surface of the optical element.
In one embodiment of the method of the invention, the adjustable focus image sensor die package is formed such that the external connection assembly is a lead frame which includes internal connection leads and external connection leads and the image sensor die is electrically coupled to the internal connection leads in a flip-chip configuration. In one embodiment of the method of the invention, the image sensor die package is formed of molded plastic, the image sensor die package being molded around a portion of the lead frame such that the portion of the lead frame is molded into the image sensor die package.
In one embodiment of the method of the invention, the adjustable focus image sensor die package is formed to further include a base, the optical element support housing being positioned on the base and the optical element support aperture is formed to have a diameter that is smaller than a diameter of the optical element support housing aperture and the optical element support is positioned within the optical element support housing. In one embodiment of the method of the invention, the optical element support is movable with respect to the optical element support housing along the optical centerline, thereby allowing a focal point of the optical element to be adjusted.
In one embodiment of the method of the invention, the optical element support and the optical element support housing are formed with threads such that the optical element support and the optical element support housing are threadably attached, thereby allowing the focal point of the optical element to be adjusted by rotating the optical element support around the optical centerline related to the optical element support housing.
In one embodiment of the method of the invention, the adjustable focus image sensor die package is formed such that the external connection assembly is a land grid array which includes internal connection points and external connection points and the image sensor die is electrically coupled to the internal connection points in a flip-chip configuration.
In one embodiment of the method of the invention, the adjustable focus image sensor die package is formed of molded plastic, the image sensor die package being molded over the land grid array such that the land grid array is formed on a first surface of the image sensor die package.
In one embodiment of the method of the invention, the molded adjustable focus image sensor die package is formed to further include a base and the land grid array is formed on a first surface of the image sensor die package base and the optical element support housing is positioned on a second surface of the base, opposite the first surface of the base.
In one embodiment of the method of the invention, the optical element support is movable with respect to the optical element support housing along the optical centerline, thereby allowing a focal point of the optical element to be adjusted. In one embodiment of the method of the invention, the optical element support and the optical element support housing are formed with threads such that the optical element support and the optical element support housing are threadably attached, thereby allowing the focal point of the optical element to be adjusted by rotating the optical element support around the optical centerline relative to the optical element support housing.
These and other features and advantages of the present invention will be more readily apparent from the detailed description set forth below taken in conjunction with the accompanying drawings.